1. Field of the Invention
The present invention relates to an optical disc device on which a CD (Compact Disc), a hybrid SACD (Super Audio CD) and a DVD (Digital Versatile Disc) can be selectively loaded. More particularly, the invention relates to a focus searching method of quickly performing a focus search, in which presence or absence detection of an optical disc and type detection thereof are performed, at the time of device starting, and an optical disc device.
2. Description of the Related Art
Generally, an optical disc has been in wide use as it enables recording information signals such as video information, audio information or computer data on a track helically or concentrically formed on a disc substrate at a high density and high-speed access to a desired track when an information signal is recorded or reproduced from a recorded track.
Now, optical discs can be largely classified into a read-only type and a recordable type. In the case of the optical disc of the read-only type, a concave-convex pit row of tracks is helically or concentrically formed on a disc substrate by injection molding that uses a resin material, and a reflection film of aluminum or the like is attached on the concave-convex pit row to form a signal surface.
On the other hand, in the case of the optical disc of the recordable type, a track is previously formed of concave-convex grooves and lands helically or concentrically formed beforehand on a disc substrate by injection molding that uses a resin material, and a recording film and a reflection film are sequentially attached on the grooves and the lands to form a signal surface.
Then, the optical disc of the read-only type reproduces data in the following manner. The signal surface is irradiated with a laser beam for reproduction which is emitted through an objective lens from an optical pickup disposed in an optical disc device to be movable in a diameter direction of the optical disc, and a return light beam reflected from the signal surface is received by a photodetector.
On the other hand, the optical disc of the recordable type records an information signal on the recording film of the signal surface by a laser beam for recording which is emitted through an objective lens from an optical pickup disposed in an optical disc device to be movable in a diameter direction of the optical disc, and then reproduces the signal from the recorded signal surface by a laser beam for reproduction as in the above case.
Regarding compact discs (CDs) among the optical discs, there are a read-only disc on which music information has been recorded, a read-only CD-read only memory (CD-ROM) on which computer data has been recorded, a recordable/reproducible CD-recordable (CD-R) on which an information signal can be recorded only once, a recordable/reproducible CD-rewritable (CD-RW) on which the information signal can be recorded by a plurality of times, and the like. These optical discs are treated as CDs since CD signal surfaces are formed in positions apart by about 1.2 mm from beam incident surface of a disc substrate.
Further, there is a super audio CD (SACD) that employs a recently developed 1-bit direct stream digital technology. In the case of this SACD, an HD signal surface is formed in a position apart by about 0.6 mm from a beam incident surface of a disc substrate, and the HD signal surface cannot be played back by a general CD player. However, in the case of a hybrid SACD that has a CD signal surface formed in a position apart by about 1.2 mm from a beam incident surface of a disc substrate in addition to an HD signal surface described above, the SACD is treated as a CD based on the CD signal surface. This enables playing-back the CD signal surface even by the general CD player.
On the other hand, regarding digital versatile discs (DVDs) higher in recording density than CDs, there are a read-only disc for reproducing a digitized and compressed video or audio, a read-only DVD-read only memory (DVD-ROM) on which computer data has been recorded, a recordable/reproducible DVD-recordable (DVD-R) on which an information signal can be recorded only once, a recordable/reproducible DVD-rewritable (DVD-RW) and a DVD-random access memory (DVD-RAM) on which the information signal can be recorded by a plurality of times, and the like. These optical discs are treated as DVDs since DVD signal surfaces of one or two layers are formed in positions apart by about 0.6 mm from a beam incident surface of a disc substrate.
Note that, for the signal surface formed on the optical disc, while there are a read-only type and a recordable type as described above, because a laser beam for reproduction is used when a type of an optical disc is detected, description below will be made focusing on a case of reproduction.
FIGS. 1A to 1D are schematic views explaining types of optical discs: FIG.1A shows a CD, FIG.1B shows a hybrid SACD, FIG. 1C shows a DVD-SL in which a signal surface is a one layer type, and FIG.1D shows a DVD-DL in which a signal surface is a two layer type.
First, as shown in FIG. 1A, a CD (Compact Disc) 10 is constituted in a following manner. A disc substrate 11 is formed in a disc shape at a diameter of about 120 mm, a diameter of a center hole of 15 mm, and a substrate thickness of about 1.2 mm by using a transparent resin material. A CD signal surface 12 is formed in a position apart by about 1.2 mm from a beam incident surface 11a on the transparent disc substrate 11 by setting a pit width and a track pitch larger than those of a DVD, which will be described later, and attaching a total reflection film, and further a protective film 13 is attached on the CD signal surface 12.
Then, in the case of playing back the CD 10 by an optical pickup (not shown) in an optical disc device, the CD signal surface 12 is irradiated with a laser beam L1, of which a wavelength has been narrowed by an objective lens OB1 having a numerical aperture (NA) of 0.45 nearly to 780 nm from the beam incident surface 11a side of the transparent disc substrate 11, and the CD signal surface 12 is played back by a return light reflected thereon.
Next, as shown in FIG. 1B, a super audio CD (hybrid SACD) 20 is constituted as a hybrid optical disc in which the disc substrate 11 of the CD 10 is divided into two in a thickness direction, and an HD signal surface 22 is added to a middle part of a CD signal surface 25 in addition to a CD signal surface 25 of an upper surface side.
More specifically, the hybrid SACD 20 is constituted in the following manner. First and second disc substrates 21, 24 having a thickness of about 0.6 mm, respectively, are stuck together to form a disc of about 1.2 mm in total thickness by using transparent resin materials. An HD signal surface 22 that employs a one bit direct stream digital technology is formed in a position apart by about 0.6 mm from a beam incident surface 21a on the lower first disc substrate 21 by setting a pit width and a track pitch smaller than those of the CD 10 and attaching a semi-transmissive reflection film, and a protective film 23 is formed on the HD signal surface 22. A CD signal surface 25 is formed in a position apart by about 1.2 mm from the beam incident surface 21a on the upper second disc substrate 24 by setting a pit width and a track pitch larger and attaching a total reflection film as in the case of the CD 10, and further attaching a protective film 26 on the CD signal surface 25.
In the case of playing back the hybrid SACD 20, the HD signal surface 22 is irradiated with a laser beam L2, of which a wavelength has been narrowed by an objective lens OB2 having a numerical aperture (NA) of 0.5 to 0.6 to nearly 650 nm, from the beam incident surface 21a side of the lower transparent first disc substrate 21, and the HD signal surface 22 is played back by a return light reflected thereon. The CD signal surface 25 is irradiated with a laser beam L1, of which a wavelength has been narrowed by an objective lens OB1 having a numerical aperture (NA) of 0.45 to nearly 780 nm and which has been transmitted through the HD signal surface 22, from the beam incident surface 21a side, and the CD signal surface 25 is played back by a return light reflected thereon.
Next, as shown in FIG. 1C, a digital versatile disc-single layer (DVD-SL) 30 in which a signal surface is one layer type is constituted in the following manner. A disc substrate 31 having a thickness of about 0.6 mm and a reinforcing disc substrate 34 having a thickness of about 0.6 mm are stuck together by use of a resin material to form a disc having about 1.2 mm in total thickness. A DVD signal surface 32 is formed in a position apart by about 0.6 mm from a beam incident surface 31a on the lower disc substrate 31 by setting a pit width and a track pitch smaller than those of the CD 10 and attaching a total reflection film, and a protective film 33 is formed on the DVD signal surface 32.
Then, in the case of playing back the DVD-SL 30 in which the signal surface is one layer type, the DVD signal surface 32 is irradiated with a laser beam L2, of which a wavelength has been narrowed by an objective lens OB2 of a numerical aperture (NA) of 0.5 to 0.6 to nearly 650 nm, from the beam incident surface 31a side of the transparent disc substrate 31, and the DVD signal surface 32 is played back by a return light reflected thereon.
Next, as shown in FIG. 1D, a digital versatile disc-dual layer (DVD-DL) 40 in which a signal surface is two layer type is constituted in the following manner. First and second disc substrates 41, 46 set to about 0.6 mm in thickness are stuck together to form a disc of about 1.2 mm in total thickness by using transparent resin materials. A first DVD signal surface 42 is formed in a position apart by about 0.6 mm from a beam incident surface 41a on the lower first disc substrate 41 by setting a pit width and a track pitch smaller than those of the CD 10 and attaching a semi-transmissive reflection film, and a protective film 43 is formed on the first DVD signal surface 42. A second DVD signal surface 45 is formed on the upper second disc substrate 46 close to the first DVD signal surface 42 by setting a pit width and a track pitch smaller than those of the CD 10 and attaching a total reflection film, and a protective film 44 is attached below the second DVD signal surface 45.
Then, in the case of playing back the DVD-DL 40 in which the signal surface is two-layer type, the first DVD signal surface 42 or the second DVD signal surface 45 is irradiated with a laser beam L2, of which a wavelength has been narrowed by an objective lens OB2 of a numerical aperture (NA) of 0.5 to 0.6 to nearly 650 nm, from the beam incident surface 41a side of the transparent first disc substrate 41, and the first DVD signal surface 42 or the second DVD signal surface 45 is played back by a return light reflected thereon.
Incidentally, there are a device and a method for identifying an optical carrier, which can identify a type of an optical disc by selectively loading one of the CD 10, the hybrid SACD 20 and the DVD-SL 30 in which the signal surface is the one layer type, and using a detection signal from a photodetector disposed in an optical pickup (e.g., see pp. 2 to 6, FIG.3 of Japanese Patent Application Laid-Open No.2000-293932).
FIG. 2 shows principle waveform charts for explaining a device and a method for identifying a carrier according to a conventional art.
The conventional carrier identifying device and method shown in FIG. 2 are disclosed in the above Japanese Patent Application Laid-Open No. 2000-293932. Here, description will be made briefly by referring to this Publication and FIGS. 1A to 1D and FIG. 2.
According to the conventional optical carrier identifying device and method disclosed in the Japanese Patent Application Laid-Open No.2000-293932, as shown in (a) of FIG. 2, an objective lens disposed in an optical pickup is raised or lowered by a focus search driving signal relative to an optical disc mounted on a turntable.
During playing-back of the optical disc, a return light from a signal surface of the optical disc is received by a plurality of photodetection areas A to D in a photodetector disposed in the optical pickup and, subsequently, photodetection amounts of the plurality of photodetection areas A to D are all added to generate an all sum signal AS (described as a pull-in signal PI in the Publication). At this time, all sum signal AS=(A+B+C+D) is set.
Now, as shown in (b) of FIG. 2, in the case of playing back the CD 10 as an optical disc, since there is a roughly 1.2 mm distance from the beam incident surface 11a of the disc substrate 11 to the CD signal surface 12, all sum signals AS appear at positions I, III of the beam incident surface 11a and the CD signal surface 12. A identification signal DD similar to that shown in (c) of FIG. 2 is obtained when comparison is made to determine whether values of the all sum signals AS exceed a threshold value TH or not. Then, a pulse interval t1 between the two all sum signals AS is measured to identify the optical disc as a CD.
Next, as shown in (d) of FIG. 2, in the case of playing back the DVD-SL 30 in which the signal surface is one layer type as an optical disc, since there is a roughly 0.6 mm distance from the beam incident surface 31a of the first disc substrate 31 to the DVD signal surface 32, all sum signals AS appear at positions I, II of the beam incident surface 31a and the DVD signal surface 32. A identification signal DD similar to that shown in (e) of FIG. 2 is obtained when comparison is made to determine whether values of the all sum signals AS exceed a threshold value TH or not. Then, a pulse interval t2 between the two all sum signals AS is measured to identify the optical disc as a DVD. In this event, for example, if time tTH is held as a reference value which is an intermediate value between the measured values t1 and t2, a measured value tx is compared with the time tTH to determine whether the measured value tx is t1 or t2. That is, it is possible to identify whether the optical disc is a CD 10 or a DVD-SL 30.
Next, as shown in (f) of FIG. 2, in the case of playing back the hybrid SACD 20 as an optical disc, since the HD signal surface 22 is at a position of about 0.6 mm from the beam incident surface 21a of the first disc substrate 21, and the CD signal surface 25 is located apart by about 0.6 mm from this HD signal surface 22, all sum signals AS appear at positions I, II, III of the beam incident surface 21a, the HD signal surface 22 and the CD signal surface 25. A identification signal DD similar to that shown in (g) of FIG. 2 is obtained when comparison is made to determine whether values of the all sum signals AS exceed a threshold value TH or not. Then, pulse intervals t3, t4 among the three all sum signals AS are measured to identify the optical disc as a hybrid SACD.
Meanwhile, according to the optical carrier identifying device and method disclosed in the Japanese Patent Application Laid-Open No. 2000-293932, when the types of the CD 10, the DVD-SL 30 in which the signal surface is one layer type, and the hybrid SACD 20 are identified, a laser beam is focused on a signal surface of an optical disc in the middle of raising or lowering the objective lens placed on standby at a lens midpoint between a lower lens bottom point and an upper lens top point based on a focus search driving signal. However, generally since the lens bottom point of the objective lens is set to a lower position sufficiently apart from the optical disc while the lens top point of the objective lens is set to a position slightly before the objective lens abuts on a beam incident surface of the optical disc, the moving distance of the objective lens at the time of the focus search is long and therefore it takes long time for the objective lens to move, which is a problem.